Background: Clear cell odontogenic carcinoma (CCOC) is a rare malignant neoplasm. They have tendency for recurrence and capacity to metastasise, yet there is very little known regarding the avidity of these lesions for FDG-PET nor the role of FDG-PET in staging and follow up of these tumours. The literature to-date mentions use of CXR, abdominal ultrasound, CT and bone scan to investigate for metastases in CCOC, however do not present FDG-PET findings in detail.

Methods: We present two cases of CCOC with their relevant PET findings.

Principle Findings: The first patient had primary CCOC of the mandible that was PET positive, and another patient had recurrence of CCOC of the anterior mandible and superomedial orbit that was not FDG-PET avid.

Discussion: Clinical application of FDG-PET in head and neck cancer mainly includes assessment of primary tumours before treatment, and to assess recurrence and response to treatment. The avidity of CCOC for PET scan is unknown. In our cases, the first patient had a left mandibular mass exhibiting intense, slightly irregular FDG uptake that was later biopsy confirmed as CCOC. However, in the second case FDG-PET failed to identify the biopsy proven CCOC malignancy of the left posterior maxilla, nor did it identify the superomedial orbital lesion that was suspicious for malignancy. However the CT scan clearly demonstrated these lesions that were later confirmed as recurrence. This raises concern that FDG-PET has low sensitivity to detect metastatic spread of this lesion. Molecular studies investigating glucose metabolism in CCOC cell may help explain this. 

Conclusion: The use of FDG-PET in staging of CCOC is questionable. Although FDG-PET is useful in other head and neck cancers and has benefits compared to other imaging modalities, further studies are needed to investigate the sensitivity of FDG-PET in CCOC.